Conventional brake systems comprise a brake caliper, a disc made of cast iron or steel and brake linings which predominantly comprise friction materials bound with phenolic resins or sintered metals. If the metallic brake disc is replaced by ceramic systems, in particular by brake discs made of C/SiC (ceramic which is reinforced with carbon fibers and whose matrix comprises silicon carbide together with elemental silicon and residues of unreacted carbon), the surface temperature of the brake disc and of the brake lining is increased by at least 200 K due to higher coefficients of friction, lower thermal conductivity and lower heat capacity of the disc. The wear of conventional brake linings increases greatly as a result of the high temperatures. Brake linings bound with phenolic resin are subject to thermal decomposition, while sintered metal brake linings melt at the surface. These disadvantages can be avoided when brake linings which can meet the increased thermal demands of the systems with ceramic brake discs are employed.
The use of fiber-reinforced C/SiC brake linings in conjunction with ceramic brake discs made of C/SiC is known from the patent application DE-A 197 27 586. The essential element of that invention is the use of the same material for both friction partners, viz. brake disc and lining. C/SiC brake discs are thus paired with a brake lining of the same type. However, the brake lining should have a lower hardness than the corresponding brake disc. This is achieved by the C/C body of the brake lining having a higher density before silicization than that of the brake disc, as a result of which it has a lower SiC content after silicization. The fibers of the brake lining are preferably aligned isotropically, as a result of which a uniform thermal conductivity transverse to the brake surface is said to be achieved.
In high-performance brake systems comprising ceramic brake discs and ceramic brake linings, the linings absorb comparatively high braking energies, resulting in considerable heating of the brake lining. While the lining material is generally designed for high operating temperatures, it is technically difficult also to design the brake shoe, the lining support and the brake piston in such a way that these will withstand high operating temperatures. In particular, prolonged thermal stress leads to overheating of the brake liquid and the elastomer rings around the pistons.